We study with intracellular electrodes the ionic mechanism of response of two types of bipolar cells, which are on-center type and off-center type. Each of these bipolar cells receives inputs from both rods and red cones, but by proper control of light stimulus and of the state of adaptation of the retina, effects of rod input and cone input on these bipolar cells can be separately analyzed. Our results so far suggest that: (1) in on-center bipolar cells their response consists of two components, one of which is mediated by Na ion and specific to rod pathways and the other by K ion and/or Cl minus and specific to cone pathways, but (2) in off-center bipolar cells their response consists of only one component which is Na ion-mediated and common to rod and cone pathways. Both types of bipolar cells mentioned above respond also to polarization of horizontal cells by current in such a way that the responses can be well accounted for by assuming that a polarization of horizontal cells exerts effects to bipolar cells indirectly via photoreceptors, though it is difficult to exclude completely a possibility of direct horizontal-bipolar pathways.